Gear pump with trapping reliefs



Fell 1967 E. ca. LITTLEWOOD 39 GEAR PUMP WITH TRAPPING BELIEFS Filed April 20, 1964 2 Sheets-Sheet 1 F851 1957 E. G. LITTLEWOOD GEAR PUMP WITH TRAPPING BELIEFS 2 Sheets-Sheet 2 Filed April 20, 1964 (6 WW m United States Patent ice 3,303,792 GEAR FUMP WITH TRAPPlNG RELHEES Elroy G. Littlewood, Prophetstown, 113., assignor to Roper Industries, inc, Rockford, ill, a corporation of Illinois Filed Apr. 29, B64, Ser. No. 360,854 2 Ciairns. (6:1. 1(l3--l2) This invention relates to fiuid pumps or motors and more particularly to a gear type pump or motor with trapping reliefs.

When the teeth on a gear pump or motor move into meshing engagement, the gear teeth engage along a line of action extending through the pitch point of the gears, and fluid is entrapped into the intertooth spaces on the drive and driven gears in the region between the line of action and the roots of the teeth on the drive gear and also between the line of action and the roots of the teeth on the driven gears. As the entrapped pockets move from the outlet side of the mesh point toward the axial plane through the gear axes, the volume of the entrapped pocket decreases and, as the pockets move away from the axial plane toward the inlet side of the pump, the volume of the pockets increases. Various different forms of trapping relief recesses have heretofore been provided in the faces of the pump housing that engage the ends of the gears, for the purpose of avoiding buildup of excessive pressures in the contracting tooth spaces at the outlet side of the mesh point, and also to aid in filling the expanded tooth spaces at the inlet side of the mesh point. However, these trapping relief recesses, in so far as the inventor is aware, have been located so as to extend into the area adjacent the roots of the teeth on the gears, that is into the area between the line of action of the gears and the dedendum circles of the gears.

An important object of this invention is to provide a pump with an improved trapping relief arrangement which effectively relieves trapped fluid in the tooth spaces and which yet avoids loss in volumetric efficiency of the pump.

Another object of this invention is to provide a gear pump in which the gears are provided with backlash so that the adjacent trapped tooth spaces in the drive and driven gears are communicated with each other through the backlash between the adjacent gears and, which pump has outlet and inlet trapping relief recesses so arranged as to relieve the fiuid from the intercommunicated trapped recesses in the drive and driven gears to the pump outlet, as the combined volume of the adjacent entrapped tooth spaces in the drive and driven gears decreases, and to relieve the adjacent rapped spaces, as the volume of these entrapped spaces increases.

A more particular object of this invention is to provide a gear pump in which the gears are provided with backlash so that the adjacent tooth spaces in the drive and driven gears are communicated with each other through the backlash between the adjacent gear teeth, and in which trapping relief recesses are provided in the housing at opposite sides of the pitch point of the gears, which trapping relief recesses are arranged relative to the line of action of the gear teeth so as to lie outside the trapped tooth spaces in the drive and driven gears, and to communicate with the trapped spaces through the backlash in the gears as the gear teeth move past the trapping relief recesses.

Yet another object of this invention is to provide a gear snares Fatentecl Pei-a. 14, 1967 pump with trapping relief recesses, and in which the relief recesses are advantageously arranged to relieve trapping of fluid between the gear teeth, when the gear teeth are rotated in either direction.

Another important feature of the present invention resides in the provision of a gear pump in which the gear teeth have backlash and in which trapping relief recesses are provided at opposite sides of the pitch point of the gears, with one edge of the trapping relief recesses extending generally along the line of action of the gear teeth.

These, together with other objects and advantages of this invention will be more readily appreciated from the following detailed description when taken in connection with the accompanying drawings wherein:

FIG. 1 is a sectional view through the pump taken on the plane 11 of FIG. 2:

FIG. 2 is a sectional view taken on the plane 2-2 of FIG. 1;

FIG. 3 is a transverse sectional view taken on the plane 33 of FIG. 1;

FIGS. 4, 5 and 6 are fragmentary enlarged sectional views through the pump adjacent the mesh point of the gears, and illustrating the gear teeth on different moved positions;

FIG. 7 is a fragmentary enlarged sectional view through the pump at the mesh point of the gears, and illustrating a modified form of trapping relief for use in pumps or motors which are rotated in only one direction.

The present invention relates to rotary gear pumps or motors hereinafter generally referred to as pumps, and particularly to a gear pump having an improved trapping relief arrangement. The trapping relief arrangement is generally ada ted for relieving the trapped fluid between pairs of meshing gears, and as shown is applied to a two gear pump, it being understood that the trapping relief recesses can also be applied between adjacent meshing gears of other multiple gear pumps, such as a three gear pump or a four gear pump.

The gear pump includes a housing or casing 1h formed with intersecting bores 11 and 12 defining a pumping cavity and having flow passages 21 and 22 communicating with opposite sides of the cavity. The pump casing may be constructed in any suitable manner and, as shown, includes end plates 13 and 14 which are secured to opposite ends of the pump housing as by fasteners 15. A pair of intermeshing gears 17 and 18 are disposed in the pumping cavity and have shafts or trunnions i9 and 2%) respectively. The pump housing has end wall means 23 and 24 engaging opposite ends of the gears 17 and 18 in close running fit therewith and the gears are conveniently supported by their shafts 19 and 2G for rotation in the end wall means about relatively parallel axes. The end wall means 23 and 24 can be formed rigidly or integrally with the housing and may, for example, form a part of the end plates 13 and 14. In the embodiment illustrated, however, the end wall means are in the form of bushings designated 26 and 27 which are disposed in the bores 11 and 12 at opposite sides of the respective gears, and which have bearings such as 28, which rotatably support the gear shafts 17 and 18, respectively. As shown, the bushings 2i: and 27 are formed separate from each other and have flat chordal faces designated 26 and 27, respectively, disposed in abutting engagement in a plane tangent to the pitch point of the gears, it being apparent that the bushingsi and 27 could be formed in one piece, if desired. In order to inhibit turning of the bushing in the bores, the latter are 7 preferably keyed to the housing, as by a pin 31 (see FIG. 2).

The teeth on the gears 17 and 13 are best shown in the enlarged views of FIGS. 4, 5 and 6. In the embodiment illustrated, the gears 17 and 13 are of the same pitch diameter and have the same number of teeth, it being understood that the invention is also applicable to gears of relatively difierent diameter and having relatively difierent numbers of teeth. The gears 17 and 18 have teeth designated a and a, respectively, with tooth faces b, b, c, c of conventional involute tooth form. Thus, as indicated in FIG. 4, the gears 17 and 18 each have a base circle designated bc, be, respectively, which base circle is the circle from which the involute tooth surfaces are derived; an addendum circle, ac, ac, respectively, which addendum circle is a circle through the tips of the gear teeth; and a dedendum circle dd, dd, the dedendum circle being a circle through the roots of the teeth of the gears. The gear teeth move into intermeshing engagement as they approach an axial plane designated up through the axis of the gears 17 and 18, and the gear teeth engage along a line of action designated La when one of the gears such as the gear 13 is rotated in one direction indicated by the arrow D in FIG. 4. If the gear 18 is rotated in a relatively opposite direction, the gear teeth will engage along a second line of action designated La in FIG. 4.

As the gears rotate, the lead faces b on the drive gear 18 engage the trailing faces 0 on the other or driven gear 17. The point of contact of each tooth on the drive gear with the corresponding tooth on the driven gear defines a line of action that extends across the axial plane ap and, in involute gears, this line of action is a straight line passing through the pitch point p of the gears and tangent to the base circles of the gears. As shown in FIG. 4, the line designated La is the line of action defined by the path of contact of the involute gears, when the gear 18 is rotated in the direction indicated by the arrow D. This line of action is tangent to the base circle [70' of the drive gear at one side of the plane up and is tangent to the base circle be of the driven gear 17 at the other side of this plane. Conversely, if the direction of rotation of the gear 18 is reversed, then the faces c on the gear 18 will engage the faces 11 on the gear 17 and the path of contact between the gears will define a line of action indicated at La in FIG. 4. The second line of action is tangent to the base circle bc at the right side of the plane up and is tangent to the base circle be of the gear 17 at the other or left side of that plane. In involute gearing, the pressure angle of the gear teeth, that is the angle designated 1' in FIG. 4 between the tooth profile and a radial line at the pitch point of the gear is equal to the angle designated y in FIG. 4 between the line of action and the line tangent to the pitch circle at the pitch point of the gears. In other words, the angle between each of the lines of action La and La and the chordal faces 26 and 27' is equal to the pressure angle x of the gear teeth. The running pressure angle of involute gears is also sometimes defined as the angle whose cosine is equal to one-half of the sum of the radii of the base circles be and be divided by the working center distance of the two gears.

As will be seen from the FIGS. 46, the line of contact between two adjacent teeth a on the drive gear with corresponding teeth on the driven gear form en trapped pockets t and t in the intertooth spaces on the drive and driven gears. The volume of the pockets decreases as the pockets move toward the axial plane up and then increases as the pockets move away from the axial plane at the other side thereof. The gear teeth are formed with backlash, that is the width of the tooth spaces exceeds the thickness of the engaging teeth on the pitch circles by a small amount and this backlash is indicated by the clearance between the trailing face c of the teeth on the drive gear. For purposes of illustration, the backlash has been exaggerated somewhat in the drawings. The backlash between the gear teeth functions not only to prevent binding of the gear teeth, but also intercommunicates the pockets designated 1" in the drive gear with the pockets designated 1 in the driven gear. When the entrapped pockets t and z" are symmetrically positioned on opposite sides of the axial plane up as shown in FIG. 4, the volume of the pocket I is decreasing at substantially the same rate as the volume of the pocket I is increasing and the backlash functions to pass fluid from the decreasing pocket into the increasing pocket. However, when these entrapped pockets are not symmetrically positioned with respect to the axial plane ap, as shown in FIGS. 5 and 6, then the volume of the pockets I and 2 does not change at the same rate and in relatively opposite directions, so that it is necessary to either relieve fluid from or introduce fluid into the entrapped pockets. Thus, in the position of the gears shown in FIG. 5, the volume of the pocket t is de creasing at a somewhat more rapid rate than the volume of the pocket I is increasing and it is necessary to pass fluid from the pockets. On the other hand, when the pockets are in the position shown in FIG. 6, the volume of pocket t increases at a more rapid rate than the decrease in volume of pocket I and it is necessary to introduce fluid into the pockets.

First and second trapping relief recesses are formed in the end wall means 2.3 and 24 and are arranged to communicate the entrapped tooth spaces with the pump outlet when the volume of the entrapped pockets is decreasing, and to communicate the entrapped pockets with the inlet when the volume of the entrapped pockets is increasing. In the embodiment shown in FIGS. 1-6, the trapping relief recesses are arranged so as to relieve the trapped fluid from the pockets, when the gears are rotated in either direction. The trapping relief recesses are formed in at least one and preferably both of the end wall means 23 and 24 of the pump and, in the embodiment illustrated wherein the end wall means ineludes separate bushings 26 and 27, a first recess ineluding recess sections 41 and 41' are formed in the bushings 26 and 27 at one side of the axial plane ap and the second recess including recess sections 42 and 42' is formed in the bushings 26 and 27 at the other side of the axial plane up. As previously noted, the end wall means could be formed in one piece instead of in the separate bushings 26 and 27 and, in that event, the relief recesses have the shape of the combined sections 41, 41, and 42, 42. The relief recesses R1 and R2 in the end wall means do not extend out into communication with the roots of the teeth of the gears, but are instead arranged so as to communicate with the entrapped pockets through the backlash between the gears. Thus, the relief recess section 41' in the first trapping relief recess R1 has one edge 43 extending along the line of action La between the gears 16 and 17 when the gears are rotated in the direction indicated by the arrow D in FIGS. 4-6. The edge 43 of the relief recess 41 extends from a point adjacent the axial plane up and at an angle to the tangent plane through the pitch point of the gears to a point beyond the end of the line of contact between the gear teeth, at the outlet side of the gears. As will be seen from FIG. 4, the tooth a on the drive gear will begin to engage the tip of the tooth a on the driven gear at the point where the addendum circle ac of the driven gear intersects the line of action La. The relief recess R1 extends at least slightly beyond this point so as to communicate with the pump outlet at a point beyond the mesh point of the gears. In order to adapt the pump for operation in either direction, the other side 44 of the recess R1 is advantageously arranged to extend along the line of action La between the gear teeth, when the gears are rotated in a direction opposite the direction indicated by the arrow D.

The edge 44 of the trapping relief also extends beyond the initial point of contact between the gear teeth at the outlet side of the pump. Similarly, the other relief recess R2 has relatively converging edges designated 46 and 47 which respectively extend along the lines of action La and La, and which edges extend from a point adjacent the plane up to a point outwardly of the point where the gear teeth begin meshing engagement, when rotated in either direction.

The relief recesses can be extended all the way to the addendum circles of the gears, if desired. However, in the embodiment as shown, supplemental recesses 51 and 52 are provided in the end wall means 23 and 24 at opposite ends of the gears to aid in filling the intertooth spaces as the gear teeth approach meshing engagement and to aid in discharging fluid from the gear teeth, as the teeth move toward meshing engagement. The supplemental recesses 51 and 52, however, do not extend sufficiently close to the axial plane up to communicate with the entrapped tooth pockets 1 and t.

The relief recesses R1 and R2 are spaced apart adjacent the axial plane ap a distance at least as great as the backlash between the gear teeth so as to prevent direct communication between the relief recesses, and consequent loss in volumetric efficiency. Since the volume of the pocket t is decreasing at substantially the same rate as the volume of pocket t is increasing, when the pockets are symmetrically positioned at opposite sides of the plane up, (see FIG. 4) the spacing between the adjacent ends of the recesses R1 and R2 can be slightly greater than the width of the trapping relief to provide some overlap without causing serious trapping. This permits the wall between the recesses R1 and R2 to be sufiiciently wide to withstand the difference in pressures between the recesses.

A somewhat modified form of relief recess can be employed if the pump gears are only rotated in one direction. This modified relief recess is shown in FIG. 7. As the preceding embodiment, first and second relief recesses designated S1 and S2 are provided in one and preferably both of the end wall means 23 and 24. In this embodiment, the end wall means designated 61 is conveniently formed in one piece, instead of a two-piece bushing 26 and 27. The relief recess S1 is located at one side of the axial plane up and the relief S2 is located at the other side of that plane. Since the gears 18 and 17 are rotated in only one direction, it is only necessary to accurately position one edge of the relief recesses S1 and S2. In this embodiment, the relief recesses are conveniently in the form of a milled slot of generally uniform width.

As shown in FIG. 7, the gear 18 is a drive gear and is located in the direction located by the arrow D. The milled slot that forms the relief recess S1 has one side edge 65 disposed along the line of action La between the drive gear 18 and the driven gear 17 and the milled slot that forms the relief recess 62 similarly has one edge 66 disposed along the line of action La between the drive and driven gears. Thus, the edge 65 of the recess or slot S1 extends generally tangent to the base circle of the drive gear from a point adjacent the axial plane up to and pref erably beyond the point at which the line of action La intersects the addendum circle of the driven gear 17. The slot or recess S1 is disposed at the side of the line of action La adjacent the driven gear 17. The width of the recess or slot can be varied as desired, but is preferably arranged so that it does not extend beyond the root diameter of the driven gear. Similarly, the edge 66 of the relief recess S2 extends from the pitch point of the gears tangent to the base circle of the driven gear and the relief recess is disposed at the side of the line of action La adjacent the drive gear 18. The recess S2 also extends from a point adjacent the axial plane ap laterally of that plane and beyond the point where the line of action intersects the addendum circle of the drive gear. As in the embodiment of FIGS. 1-6, the adjacent ends of the recesses S1 and S2 are spaced apart a distance at least as large as the backlash between the gears to prevent direct communication between the recesses. Since the relief recesses are effectively disposed at relatively opposite sides of the line of action, the ends 67 and 68 of the recesses S1 and S2 can extend closely adjacent and even overlie the line of the action provided that the ends are shaped so as to underlie the teeth and prevent direct communication between the recesses through the backlash between the teeth.

From the foregoing it is thought that the construction of the pump and trapping reliefs will be readily understood. As the drive gear rotates in one direction indicated by the arrow D, fluid is drawn into the inlet passage 22 and discharged from the outlet passage 21. When the teeth are in the position shown in FIG. 5, the pocket r is decreasing at a more rapid rate than the pocket I in the driven gear is increasing, and the pockets are communicated through the backlash between the gears with the relief recesses such as R1 in FIGS. l-6 and S1 in FIG. 1 to release the entrapped fluid to the pump outlet. As the gears continue rotating, they move through the position shown in FIG. 4 in which the volumes of the pockets t and z" are changing at substantially the same rate, but in relatively opposite directions. This is the transfer point and, at that instant, the backlash between the gears moves across the sealing land between the recesses so that communication between the pockets and the recesses is momentarily cut off. As the gears continue to rotate, they move toward a position such as shown in FIG. 6. At that time, the volume in the entrapped pocket t is increasing at a more rapid rate than the volume in the pocket 2" is decreasing. The pockets are then communicated through the backlash between the gears with the other relief recesses such as R2 (FIGS. l-6) and S2 (FIG. 7) so as to supply fluid to the entrapped pockets from the pump inlet. Thus, while the combined volume of the adjacent entrapped pockets is decreasing, the pockets are vented to the pump outlet and, when the combined volume of the adjacent entrapped pockets increases, the pockets are vented to the inlet. The relief recesses R1 and R2 in the embodiment of FIGS. l-6 are arranged to relieve the entrapped fluid, when the pump gears are rotated in either direction. In the embodiment of FIG. 7, the relief recesses are arranged so as to relieve entrapped fluid only when the pump is rotated in one direction.

While the invention has been described and illustrated in preferred embodiments thereof, it is to be understood that changes may be made in minor details of construction and adaptations to different fluid pumps or motors, without departing from the spirit of the invention or the scope of the appended claims.

I claim:

1. A fluid pump or motor comprising, a housing providing a pumping cavity having first and second flow passages communicating with the pumping cavity, a pair of meshing gears in said cavity supported for rotation about relatively parallel axes, said housing having end wall means disposed in close running fit with the ends of the gears, said gears having gear teeth in meshing engagement along one line of action when the gears are rotated in one direction and along a second line of action when the gears are rotated in the opposite direction, said end wall means having first and second trapping relief recesses located at relatively opposite sides of the pitch point of the gears and each communicating with a respective one of said flow passages, said relief recesses each having relatively converging side edges extending substantially along the first and second lines of action of the gears, said gears having backlash allowing communication between the roots of the gear tooth spaces and said relief recesses, said recesses having their adjacent ends spaced apart a distance at least as great as the backlash between the gears to prevent direct communication between the recesses.

2. A fluid pump or motor comprising a housing providing a pumping cavity having first and second flow passages communicating with the pumping cavity, first and second meshing gears in said cavity supported for rotation about relatively parallel axes, housing having end wall means disposed in close running fit with the ends of the gears, said end Wall means having first and second trapping relief recesses disposed at relatively opposite sides of an axial plane through the gear axes and communicating with a respective one of said flow passages, said relief recesses each having first and second relatively converging side edges disposed along lines extending through the pitch point of the gears and tangent to the base circles of respective ones of said first and second gears, said gears having backlash allowing communication between the roots of the gear tooth spaces and said relief recesses, said relief recesses being spaced apart at the pitch point of the gears a distance at least as great as the backlash of the gears to prevent direct communication between the recesses.

References Cited by the Examiner UNITED STATES PATENTS 1,129,090 2/1915 Hawley l03l26 2,870,720 1/1959 Lorenz 103-426 2,884,864 5/1959 Bobnar 103-426 2,990,783 7/1961 Oliver 103126 3,130,682 4/1964 Meads 103-126 FOREIGN PATENTS 578,809 7/1946 Great Britain.

DONLEY J. STOCKING, Primary Examiner.

SAMUEL LEVINE, MARK NEWMAN, Examiners.

W. L. FREEH, Assistant Examiner. 

1. A FLUID PUMP OR MOTOR COMPRISING, A HOUSING PROVIDING A PUMPING CAVITY HAVING FIRST AND SECOND FLOW PASSAGES COMMUNICATING WITH THE PUMPING CAVITY, A PAIR OF MESHING GEARS IN SAID CAVITY SUPPORTED FOR ROTATION ABOUT RELATIVELY PARALLEL AXES, SAID HOUSING HAVING END WALL MEANS DISPOSED IN CLOSE RUNNING FIT WITH THE ENDS OF THE GEARS, SAID GEARS HAVING GEAR TEETH IN MESHING ENGAGEMENT ALONG ONE LINE OF ACTION WHEN THE GEARS ARE ROTATED IN ONE DIRECTION AND ALONG A SECOND LINE OF ACTION WHEN THE GEARS ARE ROTATED IN THE OPPOSITE DIRECTION, SAID END WALL MEANS HAVING FIRST AND SECOND TRAPPING RELIEF RECESSES LOCATED AT RELATIVELY OPPOSITE SIDES OF THE PITCH POINT OF THE GEARS AND EACH COMMUNICATING WITH A RESPECTIVE ONE OF SAID FLOW PASSAGES, SAID RELIEF RECESSES EACH HAVING RELATIVELY CONVERGING SIDE EDGES EXTENDING SUBSTANTIALLY ALONG THE FIRST AND SECOND LINES OF ACTION OF THE GEARS, SAID GEARS HAVING BLACKLASH ALLOWING COMMUNICATION BETWEEN THE ROOTS OF THE GEAR TOOTH SPACES AND SAID RELIEF RECESSES, SAID RECESSES HAVING THEIR ADJACENT ENDS SPACED APART A DISTANCE AT LEAST AS GREAT AS THE BACKLASH BETWEEN THE GEARS TO PREVENT DIRECT COMMUNICATION BETWEEN THE RECESSES. 